Naphthenic acids and their derivatives are discussed in the article "Naphthenic Acid" by Edgar S. Lower, published in Specialty Chemicals, Vol. 7, No. 2, pages 76-82. This article sets forth the chemical and physical properties of naphthenic acids as well as the various procedures for the refining and purification of these acids. The article further discloses the general uses of naphthenic acids as being applicable in soap, in paint driers, extreme pressure additives for lubricating oils or greases, or as a chemical intermediate and solvent. Heretofore, naphthenic acids have been recovered by distillation. However, since the naphthenic acids often boil in the same range as other hydrocarbons having similar molecular weight their separation is with large amounts of contaminants or undesirable components and accordingly of low acid number.
A process for removing naphthenic acids from refinery streams by caustic washing is disclosed in an article, "Recover Naphthenic Acids Continuously" by David B. Todd and Frank C. Rac reprinted from Hydrocarbon Processing, August 1967. This process is based on continuous acidification followed by simultaneous centrifugal separation.